Unless your HVAC guys actually removed the cover of your unit and slid out or dismounted the cage, they probably don't know if the motor and/or cage need replacement.
A cage driven by a belt from a motor outside the cage that has become misaligned or out of balance would probably produce a whirling, scrapping or rubbing noise. A motor with worn bearings, either inside or outside the cage, sounds like just what is is - a noisy motor - you described your noise as a rattle.
So - I'm guessing that your unit is a "direct drive" - that is, the motor is mounted inside the cage. Different brands of motors are mounted to the cage with different sets of brackets - these attached with straps/bolts/nuts that can loosen over time. We have replaced the 1/3 HP motor on our air-handler twice - each time the motors available with the proper HP, speed(s), shaft length & diameter didn't match the last set of brackets and we had to buy new sets and/or improvise.
It is a lot easier for your HVAC guys to bring out a premounted motor in a cage that just slides into your unit and wire in the motor's color-coded 2-speed, 3-speed, single-speed wires than to disassemble it to find the exact cause of your rattle. Depending on his hourly rate and what the problem is, it might be cheaper too because it's faster.
So, if I was your HVAC person and had to give you a quote, I'd probably give you the same answers as they did - most customers just want the #!%$ thing fixed.